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Proceedings Paper

Degradation modes of cermet-based selectively solar absorbing coatings
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Paper Abstract

We have studied the degradation of cermet selectivity solar absorbing coatings produced by magnetron sputtering. The samples consisted of a reflector layer of molybdenum, a graded Mo-Al2O3 cermet layer, and an antireflection layer of aluminum oxide. The coatings were exposed to temperatures between 673 K and 1123 K in an atmosphere where the pressure was kept below 10-4 Torr. The degradation of the solar absorptance was determined as a function of time and temperature. A remarkable stability at high temperatures in vacuum is reported. The optical properties could be interpreted within a multilayer optical model employing the Bruggeman effective medium theory for the cermet layer. It was found that the metal content of the cermet layer continuously decreased as the degradation proceeded. We assume that oxygen ions move through the amorphous aluminum oxide in microchannels and subsequently oxidize the molybdenum particles in the cermet layer. Theories for oxidation by anion movement are reviewed and used in order to interpret the experimental degradation kinetics.

Paper Details

Date Published: 25 November 1992
PDF: 15 pages
Proc. SPIE 1727, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XI: Selective Materials, Concentrators and Reflectors, Transparent Insulation and Superwindows, (25 November 1992); doi: 10.1117/12.130495
Show Author Affiliations
Rafi Gatt, Chalmers Univ. of Technology (Sweden)
Gunnar A. Niklasson, Chalmers Univ. of Technology and Univ. of Gothenburg (Sweden)
Claes-Goeran Granqvist, Chalmers Univ. of Technology and Univ. of Gothenburg (Sweden)


Published in SPIE Proceedings Vol. 1727:
Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XI: Selective Materials, Concentrators and Reflectors, Transparent Insulation and Superwindows

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